1. Field of the Invention
The present invention relates to an optical lens assembly for imaging pickup, and more particularly to the optical lens assembly for imaging pickup comprised of five lens elements to provide a good image quality and reduce the total length to satisfy the specifications for electronic products.
2. Description of the Related Art
Currently, a personal computer is generally equipped with a web camera, and a mobile phone camera has become a necessary item. To meet user requirements, compact electronic products such as web cameras, mobile phone cameras, and digital still cameras tend to be developed with a thin design, and an optical lens assembly for imaging pickup is generally installed for capturing images of an object, and the optical lens assembly for imaging pickup must be installed in the thin computer, mobile phone or camera, and thus the compact and thin optical lens assembly for imaging pickup has a high demand. As the pixel of the camera keeps increasing, the optical lens assembly for imaging pickup tends to be developed with smaller volume and thickness, while meeting the user requirements by improving the resolution, the telecentricity, and the optical performance of the aberration correction.
In general, a conventional optical lens assembly for imaging pickup of a compact electronic product comes with different designs, including the two-lens, three-lens, four-lens, and five-or-more lens designs. If the imaging quality is taken into consideration, the optical lens assembly for imaging pickup with the four-lens or five-lens designs has advantages on image aberration and modulation transfer function (MTF) performance, wherein the five-lens design having a higher resolution than the four-lens designs thus being applicable for electronic products requiring the high quality and high pixels.
In various compact designs of the five-lens optical lens assembly for imaging pickup having a fixed focal length, prior arts adopt different combinations of positive and negative refractive powers and a group of stacked lens elements as disclosed in publications and U.S. Pat. Nos. 7,663,813, in which the two cemented glass lenses incur a higher manufacturing cost, and such conventional optical lens assembly for imaging pickup is unfavorable for the cost control of mass production. Another conventional technique is the combination of a first lens element with negative refractive power and a second lens element with positive refractive power as disclosed in U.S. Pat. No. 7,480,105, but such conventional optical lens assembly for image pickup cannot reduce the total length of the optical system easily to meet the requirement of the compact design.
In products such as compact digital cameras, web cameras, and mobile phone cameras, the optical lens assembly for imaging pickup requires a compact design, a short focal length, and a good aberration correction. As disclosed in U.S. Pat. No. 7,502,181, a first lens element with positive refractive power, a second lens element with negative refractive power, and a fourth lens element with negative refractive power are installed to shorten the total length of the optically system. Since the fourth lens element has a convex object-side surface and a concave image-side surface, the aberration correction can be compensated, and the surface shapes of the fourth lens element and the fifth lens element have a large change and must be matched with each other, and such requirements are unfavorable for mass production. In the description above, the conventional designs will increase the back focal length and the total length of the optical lens assembly for imaging pickup. In various different designs of the five-lens focal length optical lens assembly for imaging pickup with a fixed focal length, a first lens element having a convex object-side surface is used for decreasing the refractive angle of the incident light to avoid an excessive aberration, so as to facilitate obtaining a good balance between the effects of increasing the view angle of the system and correcting the aberration. If the complementary combination of the fourth lens element with positive refractive power and the fifth lens element with negative refractive power is adopted, the telecentric effect can be improved to facilitate reducing the total length of the optical lens assembly for imaging pickup effectively. Therefore, the present invention provides a more practical design to shorten the optical lens assembly for imaging pickup, while using a combination of refractive powers and a combination of convex and concave surfaces of five lens elements to lower the cost for mass production easily and apply the optical lens assembly for imaging pickup to compact electronic products.